Three-dimensional structures of biological macromolecules and their aggregates govern the interactions of these substances and produce the extraordinary sensitivity and selectivity of catalytic, regulatory, aggregational, and metabolic processes that constitute normal cellular growth and activity and also determine the characteristics of infectious diseases, metabolic disorders, and abnormalities in cell reproduction. Detailed information about these structures is basic to the development of an understanding of these processes at the molecular level. X-ray crystallography has provided much of the information required to solve the three-dimensional structures of macromolecules. However, the application of current techniques to several of the more complex structures has proved difficult, labor intensive, and costly. There is need for a high speed, precision X-ray area detector to acquire at high resolution digital, quantum efficient images of entire diffraction patterns, to spatial resolutions comparable with atomic scale. A shared facility for this purpose is being developed in the project now proposed for continuation, based on a xenon filled multiwire proportional chamber with spherically symmetric X-ray collection. This facility will provide economic data collection services at high rates and high resolution in both real in reciprocal space, together with rapid and flexible crystal alignment, monitoring during exposure, and on-line data reduction, for crystals of the many physiologically significant substances which have complex molecular structures and high molecular weights. These services will be made generally available to researchers in the northeastern United States who use X-ray crystallography in the study of such structures.